GPS Chip ?

There is just no way to keep furiously updating the worldwide
database all
the time without an immense cellular data volume that the users
would have
to PAY FOR.

The data required is relatively small. In densely populated areas, it
doesn't need every single BSSID, just a sampling of them.

Click to expand...

Yep.

The BSSID is 48 bits (all tolled), add L/L to 1 metre accuracy for
another 50 bits. 13 bytes of binary. A bit of wrapper and you could
do the whole thing in a very short message - even if the binary was
represented as ASCII hex or the L/L were more sloppily represented.
Maybe add a few more bits for signal strength for further analysis.[1]

So phones could cache quite a load of locations and slowly chuck them
up to Apple, Google and Skyhook every time there was a WiFi connection
w/o the user noticing much happening. With more and more generous
bandwidth terms from cellco's, it could also be done continuously in
the background in real time.

The database s/w would just need to validate or improve whatever is on
record or flag BSSID's as "too mobile, too often" to be useful.

And I doubt they have only "samplings" as it's very cheap, datawise,
to grab 'em all!

[1] Beyond that, some intelligent processing could improve the
position estimates of the WiFi stations over time.

Click to expand...

Trouble is that there is no way for an apple
device to accurately locate a bssid that it can see.

Click to expand...

If that BSSID is not already cached, then send the BSSID to the server,
which returns the estimated location of the WiFi (if previously seen and
stored in the database). Of course you need a datalink (Apple's own
Messages service could serve this - out of sight of the user) via the
data plan on the iPhone.

As to "accurately", if the various reporting iPhones get a reasonably
dispersed set of locations around the WiFi station, then the location
can be estimated as somewhere in the middle. Knowledge of signal
strength for each sampling iPhone could hone that somewhat. With a half
dozen such locations around a WiFi I'd WAGtimate 10 - 20 m accuracy for
the location of the WiFi. Of course that is not the location of the
iPhone using the WiFi as an initial source location.

IAC, knowing the position of the WiFi to within 200 metres is enough for
a good first guess and will help the GPS/GLONASS receiver correlate much
quicker.

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All things being relative - xml is generally bloaty v. the data it
represents.

Click to expand...

true but the data is still tiny. even if it's bloated by 10x, it would
be 130 bytes.

Should be. However there is a case for identifying the sampler in order
to be sure the database uses several independent samples for each BSSID
located. Would be nice to know more but there is likely no available info.

Click to expand...

apple says it is in response to a congressional inquiry (locationgate).
they're not lying.

there really isn't a need for a unique identifier since the same user
picking up the same bssid at the same location at another time would be
useful information. that doesn't mean there isn't but there probably
isn't.

There is just no way to keep furiously updating the worldwide
database all
the time without an immense cellular data volume that the users
would have
to PAY FOR.

The data required is relatively small. In densely populated areas, it
doesn't need every single BSSID, just a sampling of them.

Yep.

The BSSID is 48 bits (all tolled), add L/L to 1 metre accuracy for
another 50 bits. 13 bytes of binary. A bit of wrapper and you could
do the whole thing in a very short message - even if the binary was
represented as ASCII hex or the L/L were more sloppily represented.
Maybe add a few more bits for signal strength for further analysis.[1]

So phones could cache quite a load of locations and slowly chuck them
up to Apple, Google and Skyhook every time there was a WiFi connection
w/o the user noticing much happening. With more and more generous
bandwidth terms from cellco's, it could also be done continuously in
the background in real time.

The database s/w would just need to validate or improve whatever is on
record or flag BSSID's as "too mobile, too often" to be useful.

And I doubt they have only "samplings" as it's very cheap, datawise,
to grab 'em all!

[1] Beyond that, some intelligent processing could improve the
position estimates of the WiFi stations over time.

Click to expand...

Trouble is that there is no way for an apple
device to accurately locate a bssid that it can see.

Click to expand...

If that BSSID is not already cached, then send the BSSID to the server,
which returns the estimated location of the WiFi (if previously seen and
stored in the database).

Click to expand...

Trouble is that if that has come from just another idevice user,
that idevice had no way of determining the accurate location
of the bssid either. All it knows is its own location and the
fact that it can see the bssid and some rough idea of the
signal level.

Of course you need a datalink (Apple's own Messages service could serve
this - out of sight of the user) via the data plan on the iPhone.

Click to expand...

And would need to ensure that that is only used very
minimally in case the idevice is currently roaming or
has no data plan at all.

As to "accurately", if the various reporting iPhones get a reasonably
dispersed set of locations around the WiFi station, then the location can
be estimated as somewhere in the middle.

Click to expand...

Yes, but that is nothing like accurately locating it.

Knowledge of signal strength for each sampling iPhone could hone that
somewhat.

Click to expand...

Only somewhat tho.

With a half dozen such locations around a WiFi I'd WAGtimate 10 - 20 m
accuracy for the location of the WiFi.

Click to expand...

It would in fact be nothing like that unless the idevice
did a lot of sampling and calculation that wouldn’t
even be possible as you drive by it in your car.

Of course that is not the location of the iPhone using the WiFi as an
initial source location.

IAC, knowing the position of the WiFi to within 200 metres is enough for a
good first guess and will help the GPS/GLONASS receiver correlate much
quicker.

Click to expand...

You don’t need anything like that accuracy for that.

All you are doing is calculating what satellites should
be visible and even 1KM doesn’t change that significantly.

There is just no way to keep furiously updating the worldwide
database all
the time without an immense cellular data volume that the users
would have
to PAY FOR.

The data required is relatively small. In densely populated areas, it
doesn't need every single BSSID, just a sampling of them.

Yep.

The BSSID is 48 bits (all tolled), add L/L to 1 metre accuracy for
another 50 bits. 13 bytes of binary. A bit of wrapper and you could
do the whole thing in a very short message - even if the binary was
represented as ASCII hex or the L/L were more sloppily represented.
Maybe add a few more bits for signal strength for further analysis.[1]

So phones could cache quite a load of locations and slowly chuck them
up to Apple, Google and Skyhook every time there was a WiFi connection
w/o the user noticing much happening. With more and more generous
bandwidth terms from cellco's, it could also be done continuously in
the background in real time.

The database s/w would just need to validate or improve whatever is on
record or flag BSSID's as "too mobile, too often" to be useful.

And I doubt they have only "samplings" as it's very cheap, datawise,
to grab 'em all!

[1] Beyond that, some intelligent processing could improve the
position estimates of the WiFi stations over time.

Trouble is that there is no way for an apple
device to accurately locate a bssid that it can see.

Click to expand...

If that BSSID is not already cached, then send the BSSID to the
server, which returns the estimated location of the WiFi (if
previously seen and stored in the database).

Click to expand...

Trouble is that if that has come from just another idevice user,
that idevice had no way of determining the accurate location
of the bssid either. All it knows is its own location and the
fact that it can see the bssid and some rough idea of the
signal level.

Click to expand...

You're missing the purpose. A first fix within seconds that is within
100 metres (or 200 for that matter) of where you are is better than no
fix at all. Further, it aids the GPS/GLONASS receivers in acquiring
satellites more quickly (the correlators can be near perfectly set
resulting in far less search time). See bottom.

And would need to ensure that that is only used very
minimally in case the idevice is currently roaming or
has no data plan at all.

Click to expand...

Perhaps. On the other hand the amount of data involved is very little.

No data plan? Okay, keep the phone where it has a good view of the sky
until it eventually locks onto enough sats to track.

Yes, but that is nothing like accurately locating it.

Click to expand...

Depends on the value of accurate. I used to work with Omega/VLF
navigation systems. 1-2 NM was pretty accurate (and sufficient for long
range navigation). At night it could be as bad as 4 NM. Still - more
than sufficient for long range.

Also worked with Doppler nav. Accuracy was a function of distance flown
and depended on how good a heading source one had.

Also worked with RNAV (DME-DME) where accuracies were typically better
than 1/10 NM (185 metres).

Worked with unaided GPS before S/A was disabled. That 100 m circle
seemed damned accurate at the time.

Accuracy? What's that? Has no meaning w/o application.

Knowing where I am based on a WiFi station means I'm probably within 200
metres of the truth. Damned good first estimate for most daily needs.

Only somewhat tho.

Click to expand...

More than you'd suspect. You don't need survey accuracy - the whole
point of the WiFi aiding is a) faster acquisition of the more accurate
GPS/GLONASS and b) usable accuracy when you can't get sat signals
(indoor, in canyon, etc.)

It would in fact be nothing like that unless the idevice
did a lot of sampling and calculation that wouldn’t
even be possible as you drive by it in your car.

Click to expand...

You clearly don't understand what is happening. The iPhone is a
"sampler" and reports it's samples to the Apple server. The server
receives many reports on a given BSSID from many iPhones at different
times (dates/times). Each iPhone is reporting from a different position
and reports:
-position of the iPhone (accurately: using its GPS/GLONASS)
-BSSID of the WiFi station
-Signal strength received

So the server (given many samples over a lot of time from a distribution
around the WiFi) can estimate:

-the dispersion (was it a circle with somewhat even power
distribution from the centre of the circle? Then the WiFi is
at the centre; High accuracy.
Was it a long obloid? Then the WiFi is
perpendicular to the centre of mass of the obloid, but no
way of knowing which side of the obloid.

And again, this is most useful for a first estimate of where a phone is
when using that position. _Accuracy_ thence comes from GPS/GLONASS ...
or even trilateration from local cell towers.

You don’t need anything like that accuracy for that.

All you are doing is calculating what satellites should
be visible and even 1KM doesn’t change that significantly.

Click to expand...

It's not about "which are visible" but where they are wrt to the
receiver and most importantly (for quick acquisition) the Doppler shift
due to relative motion between the receiver and the satellite. That
allows you to align the correletor (which is a direct function of
Doppler shift) more accurately and thence be able to track the satellite
more quickly.

So, the better you know your position, velocity and time, the more
accurately you can position the correlators and the more quickly you get
a fix, thence tracking.

There is just no way to keep furiously updating the worldwide
database all
the time without an immense cellular data volume that the users
would have
to PAY FOR.

The data required is relatively small. In densely populated areas, it
doesn't need every single BSSID, just a sampling of them.

Yep.

The BSSID is 48 bits (all tolled), add L/L to 1 metre accuracy for
another 50 bits. 13 bytes of binary. A bit of wrapper and you could
do the whole thing in a very short message - even if the binary was
represented as ASCII hex or the L/L were more sloppily represented.
Maybe add a few more bits for signal strength for further analysis.[1]

So phones could cache quite a load of locations and slowly chuck them
up to Apple, Google and Skyhook every time there was a WiFi connection
w/o the user noticing much happening. With more and more generous
bandwidth terms from cellco's, it could also be done continuously in
the background in real time.

The database s/w would just need to validate or improve whatever is on
record or flag BSSID's as "too mobile, too often" to be useful.

And I doubt they have only "samplings" as it's very cheap, datawise,
to grab 'em all!

[1] Beyond that, some intelligent processing could improve the
position estimates of the WiFi stations over time.

Trouble is that there is no way for an apple
device to accurately locate a bssid that it can see.

If that BSSID is not already cached, then send the BSSID to the
server, which returns the estimated location of the WiFi (if
previously seen and stored in the database).

Click to expand...

Trouble is that if that has come from just another idevice user,
that idevice had no way of determining the accurate location
of the bssid either. All it knows is its own location and the
fact that it can see the bssid and some rough idea of the
signal level.

Click to expand...

Click to expand...

You're missing the purpose.
No.

A first fix within seconds that is within 100 metres (or 200 for that
matter) of where you are is better than no fix at all.

Click to expand...

You don’t need anything like that for the quicker first fix.

Even 1km is plenty. Even 10km is plenty for that.

Its different when there are no GPS satellites visible at all because
you are in the basement or deep within a big building.

Further, it aids the GPS/GLONASS receivers in acquiring satellites more
quickly (the correlators can be near perfectly set resulting in far less
search time). See bottom.

Click to expand...

You don’t need anything like that accuracy for that.

Perhaps. On the other hand the amount of data involved is very little.

Click to expand...

But if you don’t have a data plan, the data you do use is often
charged for in 1MB chunks so it doesn’t matter what size the
data packet actually is.

No data plan? Okay, keep the phone where it has a good view of the sky
until it eventually locks onto enough sats to track.

Click to expand...

In fact even with the data turned off it gets a very fast
GPS fix and that only matters when the phone has
been turned off or the GPS has been turned off.

Depends on the value of accurate. I used to work with Omega/VLF
navigation systems. 1-2 NM was pretty accurate (and sufficient for long
range navigation). At night it could be as bad as 4 NM. Still - more
than sufficient for long range.

Also worked with Doppler nav. Accuracy was a function of distance flown
and depended on how good a heading source one had.

Also worked with RNAV (DME-DME) where accuracies were typically better
than 1/10 NM (185 metres).

Worked with unaided GPS before S/A was disabled. That 100 m circle seemed
damned accurate at the time.

Accuracy? What's that? Has no meaning w/o application.

Click to expand...

But we are talking about the accuracy you see with GPS and
with the claimed better accuracy than that if you leave the
wifi and bluetooth on.

Knowing where I am based on a WiFi station means I'm probably within 200
metres of the truth. Damned good first estimate for most daily needs.

Click to expand...

But not as good as GPS.

More than you'd suspect. You don't need survey accuracy - the whole point
of the WiFi aiding is a) faster acquisition of the more accurate
GPS/GLONASS and b) usable accuracy when you can't get sat signals (indoor,
in canyon, etc.)

Click to expand...

Yes, but you won't get b) by signal strength sampling as you
drive past in your car.

You clearly don't understand what is happening.

Click to expand...

I do actually.

The iPhone is a "sampler" and reports it's samples to the Apple server.
The server receives many reports on a given BSSID from many iPhones at
different times (dates/times). Each iPhone is reporting from a different
position and reports:
-position of the iPhone (accurately: using its GPS/GLONASS)
-BSSID of the WiFi station
-Signal strength received

Click to expand...

I don’t believe that it does actually see many reports at all.

I know that mine doesn’t report anything when I do the
yard sale run because I can see it doesn’t use any data then.

So the server (given many samples over a lot of time from a distribution
around the WiFi) can estimate:

-the dispersion (was it a circle with somewhat even power
distribution from the centre of the circle? Then the WiFi is
at the centre; High accuracy.
Was it a long obloid? Then the WiFi is
perpendicular to the centre of mass of the obloid, but no
way of knowing which side of the obloid.

And again, this is most useful for a first estimate of where a phone is
when using that position.

Click to expand...

But the phone only uses that when its been moved
a long way turned off or with GPS disabled.

_Accuracy_ thence comes from GPS/GLONASS ... or even trilateration from
local cell towers.

It's not about "which are visible" but where they are wrt to the receiver

Click to expand...

No, because all that matters is what comes in thru the receiver.

And even 1km doesn’t change where the
satellites are wrt to the receiver anyway.

and most importantly (for quick acquisition) the Doppler shift due to
relative motion between the receiver and the satellite.

Click to expand...

That doesn’t change significantly in 1km either.

That allows you to align the correletor (which is a direct function of
Doppler shift) more accurately and thence be able to track the satellite
more quickly.

Click to expand...

Not when that doesn’t change significantly in 1km.

And that only matters when the phone has moved a
long way when turned off or with the GPS off too
because otherwise that stuff can just be calculated.

So, the better you know your position, velocity and time, the more
accurately you can position the correlators and the more quickly you get a
fix, thence tracking.

IAC, knowing the position of the WiFi to within 200 metres is enough for
a good first guess and will help the GPS/GLONASS receiver correlate much
quicker.

Click to expand...

Current location accuracy is not important for the GPS to get a fix
since you can be 10s of kilometres away and expect to see the exact same
satellites over you. (hundreds of kilometres off and some of the
satellites closer to horizon may no longer be visible).

There is just no way to keep furiously updating the worldwide
database all
the time without an immense cellular data volume that the users
would have
to PAY FOR.

The data required is relatively small. In densely populated
areas, it
doesn't need every single BSSID, just a sampling of them.

Yep.

The BSSID is 48 bits (all tolled), add L/L to 1 metre accuracy for
another 50 bits. 13 bytes of binary. A bit of wrapper and you could
do the whole thing in a very short message - even if the binary was
represented as ASCII hex or the L/L were more sloppily represented.
Maybe add a few more bits for signal strength for further
analysis.[1]

So phones could cache quite a load of locations and slowly chuck them
up to Apple, Google and Skyhook every time there was a WiFi
connection
w/o the user noticing much happening. With more and more generous
bandwidth terms from cellco's, it could also be done continuously in
the background in real time.

The database s/w would just need to validate or improve whatever
is on
record or flag BSSID's as "too mobile, too often" to be useful.

And I doubt they have only "samplings" as it's very cheap, datawise,
to grab 'em all!

[1] Beyond that, some intelligent processing could improve the
position estimates of the WiFi stations over time.

Trouble is that there is no way for an apple
device to accurately locate a bssid that it can see.

If that BSSID is not already cached, then send the BSSID to the
server, which returns the estimated location of the WiFi (if
previously seen and stored in the database).

Trouble is that if that has come from just another idevice user,
that idevice had no way of determining the accurate location
of the bssid either. All it knows is its own location and the
fact that it can see the bssid and some rough idea of the
signal level.

Click to expand...

Click to expand...

You're missing the purpose.
No.

A first fix within seconds that is within 100 metres (or 200 for that
matter) of where you are is better than no fix at all.

Click to expand...

You don’t need anything like that for the quicker first fix.

Even 1km is plenty. Even 10km is plenty for that.

Its different when there are no GPS satellites visible at all because
you are in the basement or deep within a big building.

Further, it aids the GPS/GLONASS receivers in acquiring satellites
more quickly (the correlators can be near perfectly set resulting in
far less search time). See bottom.

Click to expand...

You don’t need anything like that accuracy for that.

Click to expand...

1. You need it to know where you _are_ for your own purposes.

2. The tighter that estimate, the quicker the GPS/GLONASS are tracked.

But if you don’t have a data plan, the data you do use is often
charged for in 1MB chunks so it doesn’t matter what size the
data packet actually is.

Click to expand...

Most data plans (these days) are just how much data you use and often
are 250 MB, 500 MB, etc. It's 2014 in case you weren't looking and
that's chaning in a few hours too.

In fact even with the data turned off it gets a very fast
GPS fix and that only matters when the phone has
been turned off or the GPS has been turned off.

Click to expand...

Depends where you are (urban or real canyon's for example).

But we are talking about the accuracy you see with GPS and
with the claimed better accuracy than that if you leave the
wifi and bluetooth on.

Click to expand...

Who said that. The point of WiFi is for faster location of the phone
and to aid the GPS in faster acquisition.

But not as good as GPS.

Click to expand...

So what? It'

Yes, but you won't get b) by signal strength sampling as you
drive past in your car.

Click to expand...

Not all samples get to Apple that way. Indeed they may filter WiFi
"samples" based on the speed of the sampler to reduce error.

I do actually.

Click to expand...

You're proving you don't.

I don’t believe that it does actually see many reports at all.

I know that mine doesn’t report anything when I do the
yard sale run because I can see it doesn’t use any data then.

Click to expand...

The data is likely cached and uploaded when you access a WiFi or USB
connection to your computer.

But the phone only uses that when its been moved
a long way turned off or with GPS disabled.

Click to expand...

Sure. But the more accurately known the position of the WiFi, then the
more accurately known the position of the phone for its first fix.

No, because all that matters is what comes in thru the receiver.

And even 1km doesn’t change where the
satellites are wrt to the receiver anyway.

Click to expand...

Bzzt. See below.

That doesn’t change significantly in 1km either.

Click to expand...

Enough to change where the correlator is positioned.

Not when that doesn’t change significantly in 1km.

And that only matters when the phone has moved a
long way when turned off or with the GPS off too
because otherwise that stuff can just be calculated.

That is just plain wrong. 1km accuracy is plenty for that.

Click to expand...

It's plenty accurate for iPhone's, that's true. But then so is the
first fix from the WiFi location or cell tower trilateration in most use.

Current location accuracy is not important for the GPS to get a fix
since you can be 10s of kilometres away and expect to see the exact same
satellites over you. (hundreds of kilometres off and some of the
satellites closer to horizon may no longer be visible).

Click to expand...

It's true that in the context of a phone where a few seconds don't
matter that much that high accuracy won't help fast (really fast)
acquisition.

But high accuracy location of the WiFi's definitely helps in urban
canyons with the position provided by the iPhone.

What would really help get faster GPS location is if the phone gave the
GPS an indication of current speed. When traveling (even at bicycle
speed) the GPS takes longer to get a fix because it need to test wider
range of Doppler shift for each satelite (some will have frequency shift
down others go up as you more in one direction towards some and away
from others).

Obviously, the phone probably couldn't give direction of travel.

But if you donâ€™t have a data plan, the data you do use is often
charged for in 1MB chunks so it doesnâ€™t matter what size the
data packet actually is.

Click to expand...

The "default" charges when you don't have a data plan are still often in
the per kilobyte range and end up in the tens of thousands of dollars
per gig. This is one reason some carriers such as AT&T will routinely
actually disable data when they spot a user with an iPhone without a
data plan.

In an era where a plan gives you 1gb or more per month, using
inefficient XML to send data is not an issue. But for users who are
still billed by the kilobyte, then it starts to make a difference. This
is especially true since you don't even know when such data exchanges occur.

This is why when an iPhone doesn't have a data plan, you should always
disable Cellular Data, and also disable individual application's use of
data. This way, if you even need to use data to , say, send an email,
you can enable cellular data temporarily for email and be fairly
confident that a gazillion other apps won't starts to exhange data all
of a sudden.

But we are talking about the accuracy you see with GPS and
with the claimed better accuracy than that if you leave the
wifi and bluetooth on.

Click to expand...

There is no increased accuracy with wi-fi. Assisted GPS only gives you
faster access to *a* location, with no garantee that that location is
accurate until the GPS gets a location.

And even GPS locations can be inaccurate in urban canyons due to signals
bounding off buildings. My bike ride into downdown sydney has a most
interest track that skips from one block to the next (left/right travel
on straight street).

Accuracy matters if you are in a city and pull up google maps to figure
out where you are and whether you should walk left or right.

If you have been driving around, then chances are your phone has been
GPS active for quite some time, so acquisition time is not an issue.

Proper car GPS systems have software tweaked for urban canyons and
tunnels (likely with accelerometres) so they can pretend to know the
location after having lost GPS signal and can paliate for urban canyon
artifacts (it knows the car can't suddently shift from one street to the
next). I have no idea how a smalrtphoen behaves compared to caer GPS
systems in that regard.

There is just no way to keep furiously updating the worldwide
database all
the time without an immense cellular data volume that the users
would have
to PAY FOR.

The data required is relatively small. In densely populated
areas, it
doesn't need every single BSSID, just a sampling of them.

Yep.

The BSSID is 48 bits (all tolled), add L/L to 1 metre accuracy for
another 50 bits. 13 bytes of binary. A bit of wrapper and you
could
do the whole thing in a very short message - even if the binary was
represented as ASCII hex or the L/L were more sloppily represented.
Maybe add a few more bits for signal strength for further
analysis.[1]

So phones could cache quite a load of locations and slowly chuck
them
up to Apple, Google and Skyhook every time there was a WiFi
connection
w/o the user noticing much happening. With more and more generous
bandwidth terms from cellco's, it could also be done continuously in
the background in real time.

The database s/w would just need to validate or improve whatever
is on
record or flag BSSID's as "too mobile, too often" to be useful.

And I doubt they have only "samplings" as it's very cheap, datawise,
to grab 'em all!

[1] Beyond that, some intelligent processing could improve the
position estimates of the WiFi stations over time.

Trouble is that there is no way for an apple
device to accurately locate a bssid that it can see.

If that BSSID is not already cached, then send the BSSID to the
server, which returns the estimated location of the WiFi (if
previously seen and stored in the database).

Trouble is that if that has come from just another idevice user,
that idevice had no way of determining the accurate location
of the bssid either. All it knows is its own location and the
fact that it can see the bssid and some rough idea of the
signal level.

Click to expand...

You're missing the purpose.
No.

A first fix within seconds that is within 100 metres (or 200 for that
matter) of where you are is better than no fix at all.

Click to expand...

You don’t need anything like that for the quicker first fix.

Even 1km is plenty. Even 10km is plenty for that.

Its different when there are no GPS satellites visible at all because
you are in the basement or deep within a big building.

Further, it aids the GPS/GLONASS receivers in acquiring satellites
more quickly (the correlators can be near perfectly set resulting in
far less search time). See bottom.

Click to expand...

You don’t need anything like that accuracy for that.

Click to expand...

Click to expand...

1. You need it to know where you _are_ for your own purposes.

Click to expand...

That comment was about your previous purpose, acquiring
satellites more quickly. That is what the 'for that' was there for.

2. The tighter that estimate, the quicker the GPS/GLONASS are tracked.

Click to expand...

That is just plain wrong when you know where the device is to
within a few km, more accurate than that doesn’t help at all.

Most data plans (these days) are just how much data you use and often are
250 MB, 500 MB, etc.

Click to expand...

That was talking about how its charge when there is no data plan.

Depends where you are (urban or real canyon's for example).

Click to expand...

No, in both of those situations the device already knows
where the satellites are and just can't see them currently.

It is completely trivial to calculate where they have moved
to during the time that they were not visible unless the
phone has moved a long way turned off or with the GPS
turned off.

Who said that.

Click to expand...

The phone when you turn those off.

The point of WiFi is for faster location of the phone and to aid the GPS
in faster acquisition.

Click to expand...

Its also for location when the satellites are no longer
visible because you are in the basement etc.

So what? It'

Not all samples get to Apple that way. Indeed they may filter WiFi
"samples" based on the speed of the sampler to reduce error.

You're proving you don't.

The data is likely cached and uploaded when you access a WiFi or USB
connection to your computer.

Click to expand...

I know it isn't because I know when my wifi talks to apple.

Sure. But the more accurately known the position of the WiFi, then the
more accurately known the position of the phone for its first fix.

Click to expand...

That isnt true when it knows the location to within a km or few.

More accuracy than that has no effect whatever on the speed
of the first fix because none of that changes when the phone
moves by a km or few.

Bzzt. See below.

Click to expand...

Doesn’t help.

Enough to change where the correlator is positioned.

Click to expand...

No. Basic geometry.

It's plenty accurate for iPhone's, that's true. But then so is the first
fix from the WiFi location or cell tower trilateration in most use.

Click to expand...

So there isnt any point in knowing where the phone is more
accurately than that to get a faster first fix because basic
geometry means that nothing changes wrt the satellites.

There is just no way to keep furiously updating the worldwide
database all
the time without an immense cellular data volume that the users
would have
to PAY FOR.

The data required is relatively small. In densely populated
areas, it
doesn't need every single BSSID, just a sampling of them.

Yep.

The BSSID is 48 bits (all tolled), add L/L to 1 metre accuracy for
another 50 bits. 13 bytes of binary. A bit of wrapper and you
could
do the whole thing in a very short message - even if the binary was
represented as ASCII hex or the L/L were more sloppily represented.
Maybe add a few more bits for signal strength for further
analysis.[1]

So phones could cache quite a load of locations and slowly chuck
them
up to Apple, Google and Skyhook every time there was a WiFi
connection
w/o the user noticing much happening. With more and more generous
bandwidth terms from cellco's, it could also be done
continuously in
the background in real time.

The database s/w would just need to validate or improve whatever
is on
record or flag BSSID's as "too mobile, too often" to be useful.

And I doubt they have only "samplings" as it's very cheap,
datawise,
to grab 'em all!

[1] Beyond that, some intelligent processing could improve the
position estimates of the WiFi stations over time.

Trouble is that there is no way for an apple
device to accurately locate a bssid that it can see.

If that BSSID is not already cached, then send the BSSID to the
server, which returns the estimated location of the WiFi (if
previously seen and stored in the database).

Trouble is that if that has come from just another idevice user,
that idevice had no way of determining the accurate location
of the bssid either. All it knows is its own location and the
fact that it can see the bssid and some rough idea of the
signal level.

You're missing the purpose.

No.

A first fix within seconds that is within 100 metres (or 200 for that
matter) of where you are is better than no fix at all.

You don’t need anything like that for the quicker first fix.

Even 1km is plenty. Even 10km is plenty for that.

Its different when there are no GPS satellites visible at all because
you are in the basement or deep within a big building.

Further, it aids the GPS/GLONASS receivers in acquiring satellites
more quickly (the correlators can be near perfectly set resulting in
far less search time). See bottom.

You don’t need anything like that accuracy for that.

Click to expand...

Click to expand...

1. You need it to know where you _are_ for your own purposes.

Click to expand...

That comment was about your previous purpose, acquiring
satellites more quickly. That is what the 'for that' was there for.

Click to expand...

I'll grant that the accuracy doesn't have to be that great for a quicker
fix. But - it does to get you located nearby. Got off a long flight
recently?

That is just plain wrong when you know where the device is to
within a few km, more accurate than that doesn’t help at all.

That was talking about how its charge when there is no data plan.

Click to expand...

Most current smartphone users have even basic plans with gobs of data.
(it'll be 2015 here soon, not sure for you).

No, in both of those situations the device already knows
where the satellites are and just can't see them currently.

It is completely trivial to calculate where they have moved
to during the time that they were not visible unless the
phone has moved a long way turned off or with the GPS
turned off.

Click to expand...

Odd then when I'm downtown that it can take several minutes to track.

The phone when you turn those off.

Its also for location when the satellites are no longer
visible because you are in the basement etc.

I know it isn't because I know when my wifi talks to apple.

Click to expand...

Watch it constantly? Keep a log of everything?

That isnt true when it knows the location to within a km or few.

More accuracy than that has no effect whatever on the speed
of the first fix because none of that changes when the phone
moves by a km or few.

Click to expand...

It does, in fact. But I'll grant that for the time scales in question
it's meaningless.

Doesn’t help.

No. Basic geometry.

So there isnt any point in knowing where the phone is more
accurately than that to get a faster first fix because basic
geometry means that nothing changes wrt the satellites.

What would really help get faster GPS location is if the phone gave the
GPS an indication of current speed. When traveling (even at bicycle
speed) the GPS takes longer to get a fix because it need to test wider
range of Doppler shift for each satelite (some will have frequency shift
down others go up as you more in one direction towards some and away
from others).

Click to expand...

I donâ€™t see anything like that with the iphone, even tho I routinely
turn the phone off so I donâ€™t have to charge it so often. The first
fix is very fast even when I am driving around in the car.

I used to get a significant delay for first fix with the tomtom
when I turned it on and headed out in the car, but donâ€™t get
that with the iphone at all, its navigating as soon as the phone
is turned on.

Obviously, the phone probably couldn't give direction of travel.

Click to expand...

It can actually.

The "default" charges when you don't have a data plan are still often in
the per kilobyte range and end up in the tens of thousands of dollars
per gig. This is one reason some carriers such as AT&T will routinely
actually disable data when they spot a user with an iPhone without a
data plan.

Click to expand...

That is only seen much in north america.

In an era where a plan gives you 1gb or more per month, using
inefficient XML to send data is not an issue. But for users who are
still billed by the kilobyte, then it starts to make a difference.

Click to expand...

And much more when they are charged by the megabyte
even if the packet is only a few tens of bytes.

This is especially true since you don't even know when such data exchanges
occur.

Click to expand...

This is why when an iPhone doesn't have a data
plan, you should always disable Cellular Data,

Click to expand...

I donâ€™t do that and I donâ€™t have a data plan.

and also disable individual application's use of data.

Click to expand...

That doesnâ€™t in fact work with 8.1.2, it uses
the data anyway with app store updates.

This way, if you even need to use data to , say, send an email,
you can enable cellular data temporarily for email and be fairly
confident that a gazillion other apps won't starts to exhange data all
of a sudden.

Click to expand...

I donâ€™t bother and I know that none of the apps start
to exchange data as soon as I turn the cellular data on.

There is no increased accuracy with wi-fi.

Click to expand...

There is actually when the GPS satellites can no longer be seen.

Assisted GPS only gives you faster access to *a*
location, with no garantee that that location is
accurate until the GPS gets a location.

Click to expand...

It's still better than no GPS satellites visible than just dead
reckoning from the last fix when the GPS satellites were visible.

And even GPS locations can be inaccurate in urban
canyons due to signals bounding off buildings.

Click to expand...

No, GPS doesnâ€™t work like that.

My bike ride into downdown sydney has a most
interest track that skips from one block to the
next (left/right travel on straight street).

Click to expand...

I donâ€™t get that myself. There must have been something
wrong with how you were carrying the phone that prevented
it from seeing the satellites so it was guessing instead using
the wifis it could see.

Accuracy matters if you are in a city and pull up google maps to
figure out where you are and whether you should walk left or right.

Click to expand...

Yes, but it works fine in the car and is even able
to work out where you are lane wise too.

If you have been driving around, then chances are your phone has been
GPS active for quite some time, so acquisition time is not an issue.

Click to expand...

And that is true even when you haven't been driving around.

Proper car GPS systems have software tweaked for urban canyons and
tunnels (likely with accelerometres) so they can pretend to know the
location after having lost GPS signal and can paliate for urban canyon
artifacts (it knows the car can't suddently shift from one street to the
next). I have no idea how a smalrtphoen behaves compared to caer GPS
systems in that regard.

3. Why is my iPhone logging my location?
The iPhone is not logging your location. Rather, it’s maintaining a
database of Wi-Fi hotspots and cell towers around your current location,
some of which may be located more than one hundred miles away from your
iPhone, to help your iPhone rapidly and accurately calculate its
location when requested. Calculating a phone’s location using just GPS
satellite data can take up to several minutes. iPhone can reduce this
time to just a few seconds by using Wi-Fi hotspot and cell tower data to
quickly find GPS satellites, and even triangulate its location using
just Wi-Fi hotspot and cell tower data when GPS is not available (such
as indoors or in basements). These calculations are performed live on
the iPhone using a crowd-sourced database of Wi-Fi hotspot and cell
tower data that is generated by tens of millions of iPhones sending the
geo-tagged locations of nearby Wi-Fi hotspots and cell towers in an
anonymous and encrypted form to Apple.

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